Recent results indicate that hyperthermia has a promising future as a therapeutic agent by itself and as an adjunct to radiation chemotherapy. Non-toxic concentrations of the local anaesthetic procaine-HCl (Novocaine) dramatically enhances the sensitivity of mammalian cells to hyperthermia (possibly through its effects on the plasma membrane and-or associated cytoskeleton). Since less heat is required to kill cells when combined with procaine-HCl than when heat is applied alone, this anaesthetic may be useful as a tool to distinguish heat lesions resulting in cell death from heat lesions which radiosensitize cells. I propose a comprehensive quantitative and qualitative morphological study of the effects of procaine-HCl on heat killing and heat radiosensitization using synchronous populations of Chinese hamster ovary cells with the same survival value following treatments. All morphological endpoints will be compared to both survival (by colony formation) and chromosomal aberrations. The interaction of hyperthermia plus procaine-HCl with l high dose rate X-irradiation, 2) low dose rate gamma-irradiation, 3) conditions of environmental stress (low pH, low O2 concentration, and poor nutrition), and 4) a combination of "1" and "3" will be studied. Cells will be examined immediately after perturbation and for periods of time thereafter to distinguish transient lesions from irreparable lesions. The plasma membrane and its associated cytoskeleton will be the primary subcellular components studied, using time lapse cinematography, transmission electron microscopy, freeze fracture techniques, scanning electron microscopy and high voltage electron microscopy. Results from this project may 1) distinguish heat lesions responsible for cell death from those resulting in radiosensitization, and 2) lead directly to protocols using procaine-HCl with hyperthermia and radiation on animal and, ultimately, human tumors.